The present invention relates in general to spray dryers, and more particularly, to a spray nozzle assembly for injecting a slurry of finely divided material into the spray drying chamber to be contacted with a hot drying gas therein.
Spray drying is well-known in the prior art and has been used for drying solutions or slurries of finely divided particulate material dissolved or suspended in a volatile carrier liquid, most commonly water. The slurry or solution to be processed is atomized and sprayed into a hot gas stream passing through the spray dryer. The volatile carrier liquid is evaporated, and the dissolved or suspended particulate material dried to a fine powder. Spray drying has for many years been used for drying and processing food products, pharmaceuticals, and many other powder products.
More recently, spray drying has been found to be an effective method for treating flue gases from fossil fuel-fired furnaces to remove gaseous pollutants, most commonly sulfur dioxide, therefrom. In such an application, a solution or slurry of sulfur oxide absorbent, such as lime, limestone, soda ash, or caustic soda, in water is atomized and sprayed into the spray drying chamber to contact hot flue gas from the furnace. As the water in the slurry or solution is evaporated by heat from the hot flue gas, the sulfur oxide absorbent reactant contained therein reacts with sulfur dioxides contained in the flue gas. The resultant product is a dry powder of sulfur-containing salt.
A typical spray dryer generally comprises a housing defining a spray drying chamber designed to provide the proper environment and residence time for efficient drying of the solution or slurry. The drying gas is typically introduced to the vessel through an inlet at the top thereof and an outlet near the bottom thereof. The solution or slurry of particulate material to be dried is introduced into the vessel in a finely divided form through atomization means such as a spray nozzle or a disc-type atomizer. The atomized solution or slurry is sprayed into the hot drying gas as it enters the spray drying chamber so as to intermix with the hot gas so that the volatile carrier liquid is evaporated and the dissolved or suspended particulate material reduced to a fine, dry powder.
Experience has shown that it is desirable to have ready access to the atomization means to facilitate replacement and/or maintenance thereof. Slurry spray nozzles are subject to plugging by the particulate material suspended in the slurry and, therefore, must be accessible for cleaning. As disc-type atomizers are subject to severe abrasion as a result of the wearing action of the particulate material in the slurry against the surface of the atomizing wheel, they also must be accessible for inspection and maintenance. Additionally, it is desirable to have ready access to the atomization means so that the atomization means, whether it is a spray nozzle or a disc-type atomizer, may be changed in order to vary the particle size of the atomized solution or slurry as a means of controlling the characteristics of the resultant powdered product.
It is, therefore, an object of the present invention to provide an improved spray nozzle assembly wherein the atomizing spray means, whether a spray nozzle or a disc-type atomizer, may be readily removed for inspection and maintenance.